1. Field of the Invention
The present invention relates to an apparatus for reading and/or writing information on and/or from an optical card by moving in a reciprocal manner an optical head for projecting a reading and/or writing light beam and the optical card relative to each other in a track direction in which a plurality of tracks provided on the optical card extend.
2. Description of the Related Art
The optical card has a storing capacity larger than that of a magnetic card by several thousands to ten thousands times. That is to say, the storing capacity of the optical card amounts to one to two mega bytes, so that the optical card is intended to be used as various kinds of cards such as personal health managing card, prepaid card and customer managing card, although the information recorded on the optical card could not be rewritten similar to WORM (write once read many) optical disk.
There have been proposed optical cards having various track formats. For instance, in Japanese Patent Laid-open Publication Kokai Sho 63-37867, there is described an optical card, in which ID (identification) portions are provided at both ends of a track, and in Japanese Patent Laid-open Publication Kokai Sho 63-19331, there is disclosed another optical card in which a data area in a track is divided into a plurality of sectors by sector marks, each consisting of a special pit pattern which does not contain address information.
When the above mentioned optical card is used, the optical card is generally moved in the track direction in which the tracks extend to write and/or read data while the ID portions and sector marks are read out. In order to access a desired track on the optical card, a combination of a coarse access and a track jump is usually adopted. In the coarse access, an optical head including an objective lens for projecting a writing and/or reading light beam onto the optical card is moved linearly in a direction perpendicular to the track direction by means of a linear driving mechanism, while a position of the optical head with respect to the optical card is detected by means of a position detecting means such as a linear scale. Hereinafter, this direction is called a seek direction. In the track jump, the objective lens in the optical head is moved such that a beam spot formed on the optical card is moved in the seek direction track by track.
In the coarse access in which the whole optical head is moved in the seek direction, the optical head could not be moved such that the light beam spot is just made incident upon the desired track due to various factors. For instance, at a time when the optical head is initiated to be moved, the objective lens is sometimes deviated from a reference or neutral position. Further, at a time when the movement of the optical head is stopped, the objective lens is usually deviated from the reference position. Moreover, the optical card is vibrated at the end of the movement. In general, the linear moving mechanism and position detecting means have tolerances and thus the optical head could not always be stopped at a desired position. Usually a difference between a desired track and a track on which the light beam is actually made incident after the coarse access amounts to about ten tracks. In order to correct such a deviation between the desired track and the actually accessed track, the track jump is performed after the movement of the optical head in the seek direction. That is to say, the track jump is repeated by a number of times which is equal to said difference in the track addresses.
Now a known method of performing the track access or seek for an optical card shown in FIG. 1 will be explained with reference to a flow chart illustrated in FIG. 2.
As shown in FIG. 1, an optical card 1 includes an optically recordable area 3 in which a plurality of tracks 2 are arranged in parallel with each other in a track direction. At both ends of each tracks 2 there are formed ID portions 4a and 4b in which information about a relevant track is recorded. Data can be recorded in a data area 5 between the ID portions 4a and 4b.
Now it is assumed that the optical card 1 is stationary, a writing and/or reading light beam spot is formed at a point X1, and an address of a current track onto which the beam spot is made incident is known. At first, in a step S21, a difference D between the address of the current track and an address of a desired track on which the beam spot is to be moved is calculated. Then, in a step S22, an absolute value of the difference D is judged to be smaller than a predetermined threshold value a. When the absolute value of the difference D is smaller than the threshold value a, in a step S23, the track jump is performed in a desired direction. That is to say, in this case, the access time can be shortened by effecting the track jump rather than by performing the coarse access, so that the track jump is repeated by the number of times equal to the difference D. It should be noted that the threshold value a is usually set to four to ten tracks.
When the absolute value of the difference D is equal to or larger than the threshold value a, in a step S24, the coarse access is carried out by a distance equal to the difference D by moving the optical head in the seek direction. Then, the light beam spot is moved into a point X2 on the optical card 1. Next, in a step S25, the optical card 1 is moved in the track direction and in a step S26, a track address recorded in the ID portion 4b is read out. In this manner, an address of the track on which the light beam is made incident is detected. In order to read the information in the ID portion 4b of the track, it is necessary to move the optical head and the optical card relative to each other at a predetermined constant speed. To this end, the points X1 and X2 at which the track jump is performed are set to be remote from the ID portions. That is to say, after the track jump, the movement of the optical card is initiated while the light beam is made incident upon the point X2 and then the movement of the optical card is accelerated up to the given constant speed while the optical card moves over a distance between the point X2 and the ID portion 4b.
If the track access is carried out only by the track jump, in all most all cases the light beam is made incident upon the desired track. However, in the coarse access, the light beam is not made incident upon the desired track as explained above. Therefore, in a step S27, after the coarse access has been finished, it is judged whether the read out track address corresponds to the address of the desired track or not. If no, in a step S28, after the optical card 1 has been moved such that the light beam is made incident upon a point X3, after the relative movement of the optical head and the optical card has been detected to be zero and after a constant waiting time has been elapsed during which the vibration of the optical card and optical head due to the abrupt deceleration has been sufficiently dumped, the process goes back to the first step S21 and a difference D between the current track address and the desired track address is detected. It should be noted that the movement of the optical card is decelerated over a distance between the ID portion 4a and the point X3.
In this case, the difference D between the current track address and the desired track address becomes always smaller than the predetermined threshold value a, so that in the step S23, the track jump is repeated by the number of times equal to the difference D. As the result of this track jump, the light beam is made incident upon a point X4. Then, the optical card 1 is moved in the track direction to read the track address recorded in the ID portion 4a of a track and the read out track address is judged to be identical with the desired track address. When, the read out track address corresponds to the address of the desired track, in a step S30, the data is written in or read out of a data area 5 of the relevant track.
During the recording the data on the optical card and the reading the data out of the optical card, the optical card is moved in the track direction in a reciprocal manner. When the direction of the movement of the optical card is reversed, the abrupt deceleration and acceleration are required, so that not only the optical card but also the optical head are subjected to the mechanical vibration. Due to the mechanical vibration, the track jump could not be performed correctly immediately after the movement of the optical card is stopped. In order to avoid such a problem, in Japanese Patent Laid-open Publication Kokai Sho 64-27028, there is proposed to effect the track jump after the moving speed of the optical card has become substantially zero and after a predetermined waiting time period has been elapsed, the track jump is initiated as shown in the steps S28 and 29 in FIG. 2.
In the known apparatus for writing and/or reading information on and/or from the optical card, said waiting time period is set to be constant. In this case, there are two setting methods. In a first method, the waiting time period is set to be sufficiently long such that any undesired vibrations are completely dumped and the track access could be performed even in the worst case. However, in this case it is apparent that the waiting time becomes long, and therefore the access time becomes long. In a second method, the waiting time period is set to be rather short. In this case, although the access time can be shortened, it is not always possible to perform the track jump accurately and sometimes the desired track could not be accessed.